Mastitis: investigations, indications for antibiotics, and relevant research

There is no indication for midstream milk culture and sensitivities in mastitis

There is no evidence-based rationale for

• Midstream milk culture and sensitivities from a breastfeeding mother’s milk in the context of breast inflammation, even if intravenous antibiotics are indicated.

• Investigating c-reactive protein (CRP) or the full blood count (FBC), as both white cells and c-reactive protein are markers of inflammation, not necessarily infection. There is no reason to think finding elevated CRP or FBC impact positively upon treatment of breast inflammation, since this is to be expected.36, 109, 110 Kvist 2008, Angelop, kvist 2016

When are antibiotics indicated in the treatment of mastitis?

WHO declares antimicrobial resistance, which occurs in the context of antimicrobial overuse, a 'slow motion catastrophe'

Overuse of antibiotics for breast inflammation continues, in the context of the World Health Organisation’s urgent call for responsible antimicrobial stewardship, in the context of the 'slow motion catastrophe' of global antimicrobial resistance. Antibiotic over-prescribing is described as a tragedy of the commons in which a shared resource is over-exploited by some, acting in their own interests, to the eventual detriment of all.

A 2016 update of a 2013 Cochrane Systematic Review by Jahanfar et al, states: "There is insufficient evidence to confirm or refute the effectiveness of antibiotic therapy for the treatment of lactational mastitis".

Rates of antibiotic prescriptions for mastitis vary dramatically between countries

In general, doctors in my own country, Australia, prescribe more than twice the amount of antibiotics relative to our European counterparts. It is not surprising, then, that over 90% of Australian women and 86%-97% of United States women diagnosed with mastitis are prescribed antibiotics, with comparable rates in New Zealand and Canada. Scandinavian women diagnosed with mastitis or breast inflammation, however, are much less likely to be prescribed antibiotics, at 38% in a Finnish study and 15% in a Swedish study.

In the 2007 study by Kvist et al,

• 85% of 210 episodes of mastitis in 205 breastfeeding women recovered without recourse to antibiotic therapy, having received help which included a fit and hold intervention, recommendation to increase frequency of breastfeeds, and daily phone follow-up which helped women tolerate symptoms until they resolved.

• This study also showed that nipple damage did not increase the need for antibiotics, and that abscess developed in 3% of cases, regardless of antibiotic use. Abscess develops in about 3% of women diagnosed with mastitis, regardless of country or rate of antibiotic prescription.

A number of studies have shown decreased microbiome diversity and increased counts of Staphylococcus aureus in the milk of women with mastitis, but human milk microbiome research has shown that the assumption that Staphylococcus causes mastitis and must be eliminated with an antibiotic is much too simplistic.

Persistent signs and symptoms at the most severe end of the spectrum of breast inflammation may require antibiotics. You can find why the unhelpful diagnoses such infective mastitis, phlegmon, and subacute mastitis or mammary dysbiosis recommended in Clinical Protocol #36 do not help breastfeeding women, and contribute to concerning overuse of antibiotics here and here.

Antibiotics remain a treatment of last resort when signs and symptoms of breast inflammation persist without improvement after a few days, or are particularly severe and worsening.

It can help to think of a breast inflammation as a viral upper respiratory tract infection (though of course there are limitations to the analogy). The patient feels miserable for a few days, accompanied by spikes in fevers, mylagia, rigor and fatigue. As the days pass, the symptoms gradually improve and the fevers lessen. The patient might still feel unwell after three or five days, but is clearly improving. Antibiotics are not indicated.

• Fevers with breast inflammation can be expected to persist for a number of days. By 72 hours, the fevers should be lessening and the inflammation showing signs of improvement.

• By day 5, persisting fevers and no signs of improvement require antibiotic use.

• If the lump is not improving and the patient has been taking antibiotics, even with normal ultrasound, referral to the hospital for intravenous antibiotics is indicated.

Any new lump that has persisted for a week requires ultrasound, to exclude breast cancer, unless it is clinically clear that the lump is resolving and close to complete resolution. You can find out about using ultrasound to diagnose abscess here. If the lump has persisted a week but is clinically resolving, and you and the patient are happy not to ultrasound, close followup is required until complete resolution.

What antibiotics should be prescribed for mastitis when indicated?

There is an excellent downloadable pdf available if you scroll down in this module to Infant Feeding - Mastitis and Breast Abscess - Guideline, which is downloadable and contains Table 1: Recommended antibiotic regimen, available here. The guidelines for antibiotic use are:

• Flucloxacillin or dicloxacillin 500 mg 4 times daily is recommended for at least 5 days

• Cephalexin 500mg 4 times daily for at least 5 days if allergic to penicillin

• Clindamycin 450 mg three times daily for at least 5 days if the patient is known to have an anaphylactic reaction to penicillin, because of the risk of cross-reactivity between cephalexin and penicillin.

• If methicillin resistant Staphylococcus Aureus is suspected or proven, trimethoprim & sulfamethoxazole 160+800 mg bd (bactrim) or clindamycin 450 mg three times daily for 5 days are prescribed

• If breast inflammation does not improve with oral antibiotics, intravenous flucloxacillin, cefazolin or vancomycin may be necessary.

What does the research say about antibiotic use for mastitis?

Kvist et al 2007

This study seems old, but I'd argue Professor Kvist and her team's work on this topic, in multiple publications, has been a vital and still very relevant contribution to our understanding of the treatment of mastitis.

In 2007 Kvist et al’s randomised controlled trial of 210 episodes of breast inflammation in 205 lactating women concluded that daily follow-up and support while a woman awaited her body’s anti-inflammatory response was effective treatment for the great majority of lactating mothers with breast inflammation. This was regardless of how long symptomatic women waited before presenting at the midwifery clinic, which ranged from 1-7 days. That is, The time that elapsed before presenting at the clinic didn’t affect outcomes.

Women received care when they presented with any or a mix of the following: a tense breast not relieved by breastfeeding, and/or lumps in the breast tissue, breast redness, fever, or pain. The treating midwives used the term breast inflammation with patients, rather than mastitis. All women were provided with ‘essential care’, which included

• Unspecified fit and hold adjustments (though the techniques used for this fit and hold support are not described)

• Advice to decrease inter-feed intervals, that is, increase frequency of milk removal from the affected breast.36, 100, 109

Kvist reflects that with daily follow-up, women were able to tolerate systemic symptoms while resolution occurred without recourse to antibiotics. Daily follow-up also allowed detection of the 15% of patients who required antibiotics.

• 85% of 210 episodes of breast inflammation in 205 breastfeeding women recovered without recourse to antibiotic therapy.36, 100

• The presence of nipple damage did not increase the need for antibiotics.

• Women who took longer to recover had significantly higher scores for increased breast tension not relieved by breastfeeding and for erythema. But there was no difference in experience of pain between those who required antibiotics and those who didn’t. The authors concluded that clinical signs and symptoms of breast inflammation do not help clinicians make a decision about antibiotic use.36, 97, 100, 109

• The 2007 Kvist et al study found that 52% of women presented with a fever, between 1-7 days after the onset of symptoms. But there was no association between fever at presentation and the need for antibiotics.32

Kvist et al 2008

In a 2008 comparison of the milk of 192 women with mastitis or breast inflammation and 466 healthy breast milk donors, Kvist et al found no correlation between higher bacterial counts and symptoms. There were no differences in bacterial counts between those prescribed and not prescribed antibiotics or those with and without breast abscess.109

Jahanfar et al 2013

A 2013 Cochrane review by Jahanfar et al found insufficient evidence to support antibiotics in the treatment of mastitis.103

Amir et al 2024, Amir et al 2025

In Australia, a 2024 study found that 91% of GPs prescribe antibiotics when a lactating woman presents with breast inflammation. Amir et al's 2025 study of patients presenting to hospital emergency departments in Australia, Brazil, Croatia, Germany and Turkiye for lactational mastitis or abscess shows that management varied considerably between countries.

The high rates of antibiotic prescription for lactational mastitis in Australia are unsurprising as overalll antibiotic use in Australia is high relative to Europe and Canada. Australian doctors prescribe more than twice the amount of antibiotics overall compared with their European counterparts.

It's also useful to know that

• The presence of even small quantities of antibiotics in human milk alters the diversity and perhaps the resilience of the human milk and other microbiomes, and infant gut microbiota.

• PCR analysis shows that antibiotic administration reduces levels of 'friendly bacteria' Lactobacilli and Bifidobacterium in human milk.

• Cellulitis is a bacterial skin infection but mastitis is an inflammatory condition of the breast stroma, associated with secondary inflammatory changes in the skin. Cellulitis does not usually accompany mastitis.

If antibiotics are required, clinical regimens have been developed from the findings linking Staphylococcus aureus with mastitis (please see above). You can find more about the link between mastitis and S aureus here.

What are possible risks of overuse of antibiotics?

It's even reasonable to theorise, once we are informed about the underlying physiology of the milk microbiome in the context of inflammation, that inappropriate use of antibiotics might

• Prolong the episode of mastitis

• Create a more virulent mastitis. In the context of high rates of aggressive antibiotic use for lactational mastitis, it is not surprising that there has been rapid increase in the rates of MRSA identified in lactational mastitis. This is because antibiotics kill the less resistant bacteria within the microbiome. This paradoxically supports the flourishing of more resisent bacteria (e.g. multi-drug resistant S Aureus which are ironically being targeted), enhancing a resistant organism's dominance and tendency to perpetuate either prolonged infection or more virulent infection.

The rate of antibiotic use does not impact upon rates of mastitis recurrence, and the rate of abscess formation remains at approximately 3% of women diagnosed with mastitis, regardless of country or rate of antibiotic prescription for mastitis.

Recommended resources

Mastitis: prevalence, presentation, pathophysiology

Mastitis: management, consequences, prevention

Mastitis: investigations + indications for antibiotics

There is no research or biological rationale to support the belief that routine use of non-steroidal anti-inflammatories for mastitis 'treats the inflammation'

Selected references

Amir LH, Crawford SB, Cullinane M, Grzeskowiak LE. General practitioners' management of mastitis in breastfeeding women: a mixed method study in Australia. BMC Primary Care. 2024;25(161):https://doi.org/10.1186/s12875-12024-02414-12874.

Amir LH, Coca KP, Da Silva Alves MdR. Management of mastitis in the hospital setting: an international audit study. Journal of Human Lactation. 2025;4(3):401-411.

Foxman B, D'Arcy H, Gillespie B, JK B, K S. Lactation mastitis: occurrence and medical management among 946 breastfeeding women in the United States. American Journal of Epidemiology. 2002;155:103-114. 117. Wamback KA. Lactation mastitis: a descriptive study of the experience. Journal of Human Lactation. 2003;19(1):24-34.

Hill-Cawthorne G, Negin J, Capon T, Gilbert GL, Nind L, Nunn M, et al. Advancing Planetary Health in Australia: focus on emerging infections and antimicrobial resistance. BMJ Global Health. 2019;4:e001283.

Kvist LJ, Halll-Lord ML, Larsson BW. A descriptive study of Swedish women with symptoms of breast inflammation during lactation and their perceptions of the quality of care given at a breastfeeding clinic. International Breastfeeding Journal. 2007;2:2.

Kvist L, Larsson BW, Hall-Lord ML, Steen A, Schalen C. The role of bacteria in lactational mastitis and some considerations of the use of antibiotic treatment. International Breastfeeding Journal. 2008;3:6.

Soto A, Martin V, Jimenez E, Mader I, Rodriguez JM, Fernandez I. Lactobacilli and bifidobacteria in human breast milk: influence of antibiotic therapy and other host and clinical factors. Journal of Pediatric Gastroenterology and Nutrition. 2014;59:78-88.